public void ReturnsKeys() { // Arrange const string key1 = "TestKey1"; const string key2 = "TestKey2"; _sut.Clear(); var item1 = new TestObject(1, "Jane Smith"); var item2 = new TestObject(2, "John Smith"); _sut.SetItem(key1, item1); _sut.SetItem(key2, item2); // Act var keyNames = _sut.Keys().ToList(); // Assert Assert.Collection(keyNames, item => Assert.Equal(key1, item), item => Assert.Equal(key2, item)); }